System for determining tube characteristics



Oct. 16, 1951 F. M. GLASS- 2,571,439

SYSTEM FOR DETERMINING TUBE CHARACTERISTIC Filed March 10, 1950 5Sheets-Sheet l 600N715 Pi? All/V07! INVENTOR. F2070 M .7445;

Oct. 16, 1951 F. M. GLASS SYSTEM FOR DETERMINING TUBE CHARACTERISTICSFiled March 10, 1950 3 Sheets-Sheet 2 4 m m m m zayo #1 an.

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Patented Oct. 16, 1951 SYSTEM FOR DETERMINING TUBE CHARACTERISTICS FloydM. Glass, Oak Ridge, Tenn, assignor to the United States of America, asrepresented by the United States Atomic Energy Commission 7 ApplicationMarch 10, 1950, Serial No. 148,999

9 Claims.

My invention relates to systems for determining the characteristics ofradiation responsive devices, and more particularly to a system forautomatically plotting the plateau of the characteristic rise curve of aGeiger-Mu ler tube.

In general, when the potential across the counter is raised no efiectwill be noticed on the tube until the threshold voltage is reached, thena small increase in potential will cause the number of discharges orcounts per unit time to rise quite abruptly to a certain value. Anyfurther increase in the potential will cause very little change in thecounts or discharges until what may be called the maximum operatingpotential of the counter is reached. A small increase from here on willcause a sudden increase in counts, which may the tube is usuallyoperated in some intermediate portion of the plateau or range, it isimportant to know the extent of the plateau as well as the generalcharacteristic curve of the tube.

The general shape of the characteristic curve of a Geiger-Muller tube iswell known. A normal procedure for obtaining the curve is to place asource of radiations near the tube, vary the voltage on the tube fromzero to an upperlimit in a series of separate adjustments, record thecounts per minute of the output of the tube each time, and then plot thecounts as ordinates against the tube voltage as abscissa. This isgenerally carried out with a sealer circuit which counts arepresentative number of pulses at each I voltage impressed across thetube. .Since each voltage is attained through manual adjustment, a greatdeal of tim and an experienced operator are required in making thevarious counts over the voltage range of the tube, and to progressivelycollect the data for determinin the various por-' tions of the curve.The voltage limits of the plateau, referred to above, are difierent foreach tube. Accordingly it is customary to plot the plateau for each tubeto be placed in service; This plateau serves as a record of tubecharacteristics for all subsequent operations.

While some effort has been made to provide systems for automaticallyplotting the plateaus of tubes, they have been subject to the followingdisadvantages:

a. The entire plateau must be plotted at a sensitivity limited by thechange of counting rate and size of the recorder scale.

2 the Geiger-Muller tube is not variable, since the recorder motor alsodrives the voltage control potentiometer arm.

c. A recorder must be especially modified to be used with thoseinstruments, and

d. The incremental voltage must always be applied in an increasingdirection.

Applicant with a knowledge of all of these problems in the prior art hasfor an object of his invention the provision of a system forcontinuously and progressively plotting the plateau of a radiationsensitive tube.

Applicant has as another object of his invention the provision of asystem for examining any desired part of the plateau of thecharacteristic curve of a radiation sensitive tube at maximumsensitivity.

Applicant has as a further object of his invention the provision of asystem for examining the characteristics of a tube, and which is capableof applying a variable, reversible rate of change of voltage to thetube.

Applicant has as a still further object of his invention the.provisionof a system for quickly and readily examining thecharacteristics of a tube, and progressively plotting them to provide acharacteristic curve therefor.

Other objects and advantages of my invention will appear from thefollowing specification and accompanying drawings, and the novelfeatures thereof will be particularly pointed out in the annexed claims.

In the drawings, Fig. 1 is a typical characteristic curve, showing theusual plateau region, of a Geiger-Muller tube. Fig. 2 is a schematic ofmy improved system for automatically plotting the characteristic curveof a Geiger-Muller tube. Fig. 3 is a schematic of the power circuits formy improved potting system.

Referring to the drawings in detail, I designates a conventionalGeiger-Muller tube having its outer shell portion grounded and havingits center wire maintained at a predetermined positive potential by avoltage regulated supply circuit shown in detail in Fig. 3.. Thisvoltage, supply circuit includes the usual power transformer 64havingits primary connected to the 115 volt A. C. power line and having aplurality of secondary windings for supplying power to my improvedsystem. Thesecondary winding at one extremity of the transformerprovides the filament heating current for the various tubes as indicatedby :r in Fig. 2, while the secondary winding at the other end suppliesthe filament of the rectifier 65 of the power supply, as indicated inFig. 3. The intermediate secondary winding 64' is of the split typehaving its center tap grounded and the two end leads connected to theplates of the rectifier 55 whose filament is connected to one of theouter secondary windings, as heretofore indicated. The rectifier tube 65is then connected through a conventional capacitance-inductance filter86 for removing the D. C. ripple, and this filter is in turn connectedthrough a series regulator including: double triode 51 with currentlimiting resistors 88, 69 in the grid circuits thereof. The output ofthe series regulator is in turn connected through a tetrode H which actsas a voltage amplifier and also provides correct phasing. This tetrodeis fed from the unit through load resistor 'I'O and resistors 13 and 14,14' which are bridged-between the power unit and the cathode of tube Hacross voltage regulating tube 12 to provide the necessary operatingpotentials for the tube. The grid potential for the control grid oft'etrode H is determined by the voltage divider with resistors T6, T7and 19 with movable contact on resistor or potentiometer 11 serving toadjust the voltage on the control grid. Resistor 15 serves to couple thecontrol grid of the tube TI to the volta e divider, with capacitor 18bridging grid resistor 15, and the power lead serving to pass quickchanges in potential or surges to the-control grid of tube H to adjustits conductivity and provide regulation.

Voltage for the center wire of the Geiger- Miiller counter l isregulated by the adjustable resistor 2 which is in series withpotentiometer 3 whose moving contact is coupled to the high voltagesupply for the Geiger-Muller tube, as indicated hereinafter.

Int'his high voltage supply, power is fed from the power line throughleads I08 to the primary of a second power transformer 8| whichenergizes a rectifier 82 with a pairof secondary windings, and feedspower through the rectifier to a condenser 83 which acts as a filter,and a series resistor 84' which may act as a load resistor. Bridgedacross the output is a shunt voltage regulator in the form of a triode85. Bias and signal are supplied to the control grid of the triode fromsource 81' and the voltage divider 88, 4, I03 and [04 'while quickchanges in signal are applied to the grid through condenser 86 for thepurpose of regulating the output voltage fed to line 90 which suppliesthe power through switch SI and l'oadiresist'or 92 to the center wire ofthe Geiger-Muller counter 1. Meter I05, shunted by resistor I04 servesto indicate the potential of the line.

The filaments of tube 61 are energized from the secondary ofpower'tra'nsformer 89 while the filament of tube 85 is energized from athird secondary on transformer 8|. If desired, the usual VR. tube may beplaced across these secondaries to regulate the voltage.

Geiger-Muller tube -I feeds into a pulse limiting and shaping circuit.It is coupled through a condenser '93 to the control grid of the firstsectionof a duo-triode tube I which serves as a part of a univibrator.The'other portions of the univibrator include a common cathode resistor22 connecting the cathodes of tube 1 to ground, a coupling condenser 2|which couples the output of the first section of duo-triode to thecontrol grid of the second section of that tube. Potential is suppliedto the plates of the tube through load resistors and 23. A grid leakresistor 24 bridges the control grid of the second section of tube 1 andground, while the biasing potential is supplied through resistor 25 fromline 94. The resistors 24 and 25 bridged across line 94 of the lowpotential power source to ground constitutes a voltage divider fornormally maintaining the second section of tube 1 at cutoff potential.

The output of the first section of tube 1 is coupled through condenser26 to the control grid of the first section of duo-triode tube 8 whichforms a part of a second univibrator. Potential for the plates of tube 8are supplied through load resistors 32, '34 from line 94 while commoncathode resistor 31' connected from the cathodes of tube 8 to groundserves to provide a biasing potential. Voltage divider resistors 29, 28and 38 cooperate through a moving contact on resistor 28 with gridresistor 21 to provide a positive biasing on the control grid of thefirst section o'f tube '8 from: line 94. Resistor 33 bridges line 94 andthe control grid of the second section of tube 8 to provide a positivepotential greater than that of the grid of the first section of the tubeto maintain the secondsection normally operative. The cathodes of thetube are tied together and grounded through a common cathode resistor3|. The two sections of tube 8 are coupled in cascade throughcondenser36, and the output circuit of the second section "is connected through acoupling condenser 31 to the control grid of the first section ofduo-triode tube 9 which constitutes a part of a third univibrator. Loadresistors 43 and 45' serve to provide potential for the plates of thetwo sections of tube 9 from line 94, while resistors 38,39 and 41 form avoltage divider which is coupled through resistor '40 to the controlgrid of the first sectionof tube 9 to provide a positive bias. A commoncathode resistor 42 is bridged between the cathodes of tube 9 and groundwhile line or B potential is supplied to the control grid of the secondsection of tube 9 from line 94 through resistor 44. The output of thefirst section is coupled to the control grid of the second section oftube 9 through the condenser 46, and the output of the-second section oftube 9 is coupled through condenser 41 to the tube Id.

The duo-diode tube l0 serves as a rectifier for the pulses from theunivibrators which include tubes 1, Band 9. Disposition of the undesiredportion of the wave is accomplished by grounding the anode of the firstsection while tying the cathode thereof to the anode of the secondsection. In this way any undesired portion of opposite polaritycan beshunted to ground. The cathode of the second section of tube 10 feedsintoan integrating or standard rate meter circuit including condensersII and 48 and resistors l5 and 53. Condensers 48 and H may be connectedin parallel through a manually operated switch 49 and to resistors I5,53 through a resistor 52. In addition, a resistor 58 is connected intothe circuit at the juncture of the resistor 52 and condensers H, 48.Closing of switch 54 may serve to charge the condensers through line 84while the closing of switch 5| will provide a path to ground fordischarging them.

Resistor [5 takes the form of a potentiometer with its moving contactconnected to the control grid of the first section of duo-triode tube I!which forms part of a vacuum tube volt meter, with the two anodes of thetube connected through bridge resistors '51, 58 to a balancingpotentiometer 56 whosemoving contact is joined to a circuit including apotentiometer 55 connected across from line 94 to ground, and resistors6|, I3 and I00. The resistor I3 is in the form of a potentiometer withthe moving contact connected through resistor 62 to the control grid ofthe second section of tube I2. The cathodes of tube I2 are tied togetherand are coupled to ground through a cathode resistor 59. Bridged acrossthe plates of tube I2 is a meter or galvanometer I4 coupled throughduo-diode tube I6. Interposed in this circuit is a single pole doublethrow switch IOI for alternately inserting resistor 63, or aconventional recorder 5, such as an Angus recorder in the circuit. TheAngus recorder is conventional to the prior art and is made byEasterline-Angus Company, Inc.

A relay 60 controlled by switch 91 and energized from the power line I06may be employed to short out resistor 6|. In addition, a motor 3'energized through switch 95 from the conventional power line may beoperated in forward or reverse direction by single pole double throwswitch 96 which serves to change the power connections to the windings.The motor 3 may then be mechanically connected through a conventionalslip clutch (not shown) to actuate the arm of potentiometer 3, which maytake the form of a conventional Helipot.

In the operation of the system, the tube under test is subjected to astardard source of radiations and motor 3' is energized by closing theswitches 95, 96, with the moving contact of potentiometer 3 set nearground potential. As the motor, which preferably rotates at about 6 RP.M., slowly rotates, the contact on the potentiometer is slowly movedupwardly or around to increase the potential thereof above ground. Thishas the efiect of raising the potential of point I02 of the high voltagesupply source for the Geiger- Miiller tube. Increasing the potential atI02 tends to create a bucking voltage, and has the 1 effect of reducingthe potential differences or voltage drops across the voltage dividerincluding resistors 88, I03, 4, and shunt resistor I04 and meter I05.That in turn has the efiect of lowering the potential on the .controlgrid of triode 85, reducing its conductance, and in turn the drop acrossresistor 84 which increases the potential impressed across theGeiger-Muller tube I. As the motor continues rotation; the potentialacross the Geiger-Muller tube is thus progressively increased.

When switch 9| is closed, a high positive potential from lead 90 isimpressed through the load resistor 92 upon the center wire of theGeiger-Muller tube I, but this high potential is blocked from reachingthe control grid of the first section of tube I by condenser 93. Whenthe tube I is subjected to radiations from an appropriate source,negative pulses are produced at the center wire thereof and these pulsesare impressed through coupling condenser 93 upon the control grid of thefirst section of tube 1. Since the first section of the tube is normallyconducting, these negative pulses reduce the con duction or out 01? thatsection of the tube to produce positive pulses at the anode thereofwhich are passed through the coupling condenser 2I and are impressedupon the control grid of the second section of the tube to raise thegrid potential thereof and cause it to conduct. This tends to maintainthe bias produced by the voltage drop across the cathode resistor 22.After the charge is leaked off of the grid through the grid resistor 24,the second section of the tube becomes non-conducting'bias provided bycathode resistor 22 is reduced and thefirst section commences to conductagain. The length of time ducting state, that is, with the first sectionof the tube normally conducting, is determined by the constants of thecircuit. Signal in the form of a rectangular shaped pulse, substantiallyin dependent in size and configuration from the original pulsesimpressed upon the circuit, appears at the plate of the first sectionand is transferred through the coupling condenser 26 to the control gridof the first section of the duo-triode tube 8.

While the control grid of the first section of tube 8 is normallymaintained at a predetermined positive potential by virtue of thevoltage drops through'resistors 29, 28 and 30, the control grid of thesecond section of tube 8 is maintained at a substantially higherpotential by being coupled through resistor 44 to the B of line 94;Therefore, it is apparent that this latter grid, maintained at thehigher potential, will cause the second section of tube 8 to conduct inpreference to the first section, since the high positive potential onthe control grid of the second section will be sufficient to overcomethe bias introduced by the drop across cathode resistor 3|. Accordinglythe second section of the tube is normally conducting while the firstsection will remain non-conducting. However, application of the positivepulse from the plate of the first section of tube I to the control gridof the first section of tube 8 raises the potential of that grid to apoint where it overcomes the bias due to the drop through cathoderesistor 3 I. This, in turn, causes the first section of tube 8 toconduct, producing a negative pulse on the plate thereof, and thisnegative pulse passes through condenser 36 and is impressed upon thecontrol grid of the second section of that tube causing the potentialthereof to drop and permitting the cathode bias to cut it off. Thiscondition exists for the duration of the pulse, but depends on theconstants of the circuit. The cut off of the second section of tube 8produces a positive pulse at the plate thereof which is passed throughcoupling condenser 31 to the control grid of the first section of tube9. This positive pulse raises the potential of the grid thereof andovercomes the bias introduced by the drop across cathode resistor 42,causing the first section of the tube to conduct. As in the previoustube the potential of the control grid of the first section coupledthrough resistor 40 to the voltage dividers 38, 39, 4! is at a lowerpotential than the grid of the second section of the tube which iscoupled through the resistor 44 to the B power-lead 94. This produces acondition where the second section of the tube is normally conducting.In this state the positive pulse, referred to above, impressed upon thegrid of the first section of the tube through coupling condenser 31causes the potential to rise and overcomes the bias introduced by thedrop across the cathode resistor 42, causing the first section toconduct. This produces a negative pulse on the plate thereof which istransferred through the condenser 46 to the control grid of the secondsection of the tube causing its grid potential to be lowered, andpermitting the cathode bias resulting from the drop across cathoderesistor 42 to cut off the operation of the second section'of this tube.This negative pulse which drives the second section of the tube to cutoff, produces a positive pulse on the plate thereof. This positive pulseis then impressed through condenser 41 and rectifier l upon theintegrating circuit ll, 48, I5. As in the previous univibrator circuits,the duration of cut off of the second section of tube 9 will depend uponthe constants of the circuit.

It will be noted that the circuit includes three univibrators. Inproviding three univibrators in the circuit, instead of a singleunivibrator, it is possible to isolate the final output pulse from thesize and shape of the original pulse of the Geiger-Muller counter and toeliminate or reduce the effects of changes in the characteristics of thetubes. The univibrators are conventional components of a circuit, ingeneral are old and well known components in the art, and their actionand operation are described in the prior co-pending application ofParsons, S. N. 53,794.

The integrating or rate meter circuit ll, 48, I receives the rectifiedpulses from the rectifier l0. These pulses are of uniform magnitude andbuild up a charge on the condensers 48, ll of the integrating circuit.The charge built up on these condensers is continuously leaked offthrough the resistors I5, 53, and the magnitude of charge on thecondensers at any particular time is proportional to the number of thepulses reaching the integrating circuit. This rate meter circuit issimilar in principle to many others used in the field of radiationdetection and measurement, and the underlying principles thereof are setforth in an article in volume '7 of the Review of Scientific Instrumentsat page 450. r

The drop across the potentiometer I5 and resistor 53 of the integratingcircuit is applied to the control grid of the first section ofduo-triode tube 12 causing the first section of that tube to conduct.This changes the impedance of the bridge including resistors 51, 58 andthe two sections of tube I2 causing current fiow through the diode l6,meter 14, and recorder 5. This provides an indication on the meter i4and produces a record on the recorder 5 of the number of counts orpulses per unit time.

It will be apparent that as the motor 3' continues to rotate and movethe contact over the potentiometer 3, the potential impressed at line 90from the high potential source, continues to rise. This slowly increasesthe potential impressed across the Geiger-Miiller tube I and inaccordance with the characteristics of the counter changes the number ofpulses produced by it for translation through the univibrator circuits,and for application to the integrating circuit for the subsequentmeasuring and'recording by the vacuum tube volt meter and recorder. Ifthe whole characteristic curve is desired, the motor 3 is permitted tocontinue to rotate until the potentiometer 3 reaches the maximumposition covering the full voltage spectrum of the counter. After thatfurther rotation of the motor '3' does not further actuate the movingcontact of the potentiometer due to the action of the slip clutch whichpermits relative rotation between motor 3' and the moving contact of thepotentiometer. It will thus be seen that the slip clutch provides asafety feature for preventing any injury to the potentiometer or motorif the switch 92 is not opened immediately upon the moving contactreaching its upper extremity.

To quickly reach the plateau, it'may be desirable to open the switch 49since the lower capacity of the small condenser 48 permits rapidoperation to locate the threshold potential of the Geiger-Muller tube.The biasing potential on the control grid of the second section of tube[2 ismadeadjustable in orderto change the opera- 8 tion of the vacuumtube volt meter and provide a suppressed zero setting therefor. Therectifier It acts to keep the voltage off of the meter l4 and recorder 5until the time constant of the integrating circuit permits applicationof voltage to the vacuum tube volt meter.

As an alternative this system may be adapted for use in determining thecharacteristics of tubes operating in the proportional range, and mayalso be useful in examining other types of radiation detecting devices.This may be accomplished by simply interposing a conventional amplifier(not shown) between the tube l and the pulse limiting and shapingcircuit which includes tubes 1, 8 and 9. In this way selected signalsfrom the tube I in various ranges may be raised to the desired levelbefore feeding them into the pulse limiting and shaping circuit.

Having thus described my invention, I claim:

1. A system for determining the characteristics of a counter comprisinga source for applying an energizing potential across the counter and forprogressively increasing this potential over the voltage spectrumthereof, a pulse limiting and shaping circuit for receiving the outputof the counter, means for rectifying the output of the pulse limitingand shaping circuit, an integrating circuit coupled to the rectifyingmeans, and means for recording the output of the integrating circuit.

2. A system for determining the characteristics of a counter comprisinga source for applying an energizing potential across the counter and forslowly increasing the potential to progressively sweep the voltagespectrum, a pulse limiting and shaping circuit for receiving the outputof said counter, means for rectifying and integrating the output of saidpulse limiting and shaping circuit, and a vacuum tube voltmeter coupledto the rectifying and integrating means for measuring the output ofthecounter.

3. A system for determining the characteristics of a counter comprisinga source for supplying'an energizing potential across the counter andfor slowly increasing the potential to progressively sweep the voltagespectrum, a pulse limiting and shaping circuit for receiving the outputof the counter, a rectifier coupled to the output of the limiting andshaping circuit, a rate circuit for integrating the output of therectifier, and a vacuum tube voltmeter fed by the integrating circuitfor measuring the output of the counter.

4. A system for determining the characteristics of a counter comprisinga source for supplying a potential across the counter, means forcontinuously increasing the potential to sweep the voltage spectrum, apulse limiting and shaping circuit for receiving and equalizing thepulses from the counter, a rectifier coupled to the pulse limiting andshaping circuit, an integrating circuit fed by the rectifier forproviding a signal corresponding to the pulse rate from said counter, avacuum tube voltmeter circuit connected to the integrating circuit, anda recorder for measuring the output of said vacuum tube voltmetercircuit.

5. A system for determining the characteristics of a counter comprisinga source for supplying a potential across a counter, means forprogressively increasing the potential to sweep the voltage spectrum, aplurality of unii'ibrators for receiving and equalizing the pulses fromthe counter, and means for converting the output of said univibratorsinto signals corr sponding to the rate of pulses from said counter, andmeans for indicating the pulse rate.

6. A system for determining the characteristics of a counter comprisinga source for applying a potential to the counter, means for continuouslychanging the potential to sweep the voltage spectrum, a plurality ofunivibrators for equalizing the pulses from the counter, means coupledto the output of said univibrators for rectifying and integrating thesignals therefrom to produce output voltages corresponding to the pulserate of the counter, and means for indicating the pulse rate.

'7. A system for determining the characteristics of a counter comprisinga source for applying potential to the counter, means for progressivelyincreasing the potential of said source to sweep the voltage spectrum, aplurality of univibrators for receiving and equalizing the pulses fromthe counter, means coupled to the univibrators for converting theiroutput into signals corresponding to the rate of pulses from saidcounter, a vacuum tube voltmeter fed by the converting means, and

a recorder for measuring the pulse rate.

8. A system for determining the characteristics of a counter comprisinga source for applying a potential to the counter, means forprogressively increasing the potential to cover the voltage spectrum, aplurality of univibrators for receiving and equalizing the pulses fromthe counter, rectifying and integrating means coupled to theunivibrators for converting their output into signals cm- 10 Iresponding to the pulse rate of the counter, and means fed by therectifying and integrating means for recording the pulse rate.

9. A system for determining the characteristics of a counter comprisinga source of potential for the counter, power means for continuouslyadjusting the potential to sweep the voltage spectrum, a, series ofunivibrators connected in cascade for receiving and equalizing thepulses from the counter, a rectifier fed by the univibrators forrectifying the pulses, an integrating circuit cou- Dled to the rectifierfor converting the rectified pulses into signals corresponding to thepulse rate of the counter, a vacuum tube voltmeter circuit connected tothe integrating circuit, and a recorder coupled to the output of thevacuum tube voltmeter circuit for recording the pulse rate.

FLOYD M. GLASS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,491,904 Poole Dec. 20, 19492,495,072 Molloy Jan. 17, 1950 2,499,953 Herzog Mar. 7, 1950 2,506,435Rossi et al May 2, 950

